Biologist define species as groups of actually or potentially interbreding natural populations which are reproductively isolated from other such groups. This definition known as the biological species concept.
how do new species form: speciation depends on two factors: the isolation and the genetic divergence of the population. Isolation of populations and genetic divergence.
species and speciation
genetic drift
Genetic drift is one of the major mechanism of evolutionary change and has significant implications for human interactions. Different form of the same gene are known as alleles. A population is all the individuals of a species living in a particular place at a particular time. the relative proportion of an allele in a population is the allele frequently. The sum of all genes in a population is the gene pool. Hardly weinberg equilibrium is the maintained of a population is not evolving. The alleles responsible for blue color has ben lost, such loss of alleles is usually consequence of genetic bottleneck. Population bottleneck can cause all of the following except: changes in allele frequency. Loss of alleles. Reduction in genetic variability. Bottleneck happens to small population. The effects on evolution change are random. There is a loss of genetic variation after a bottleneck in our example. The allele for blue coloration was lost.
Muscle cell (myocyte, muscle fiber) anatomy:
Sarcoplasmic reticulum: specialized area of the endoplasmic reticulum
Surrounds the myofibrils like a web
At each end, forms bag-like structure “terminal cisternae”
Area where calcium (Ca2+) is stored
Transverse tubules: tube formation of the sarcolemma
Tubes run from the external surface straight through the muscle cell
Transverse tubules and terminal cisternae form a “triad” structure (many of these along the length of the muscle cell)
Muscle Physiology video
Muscle Physiology This video was made in Dr. O's A&P1 class. Make sure you answer & review the questions at the end of the video, and also the following question:
What are the functions and structure of skeletal, smooth & cardiac muscle?
sliding filament mechanism
Sliding-Filament Mechanism found in muscle. Muscle working mechanism is very interesting. A good explaining theory for this process like that.
Muscle contraction is produced by cross bridge cycles. A cycle has 4 steps:
(1) Energizing of myosin cross bridge
A + M•ATP —> A + M*•ADP•Pi (ATP is energizer here)
(2) Attachment of cross bridge to a thin filament
A + M*•ADP•Pi —> A•M*•ADP•Pi
(3) Movement of cross bridge, producing tension
A•M*•ADP•Pi —> A•M + ADP + Pi
(4) Detachment of cross bridge from thin filament
A•M + ATP —> A + M•ATP (ATP is modulator here)
Movement of the cross bridges make the overlapping thick and thin filaments slide past each other (they do not change in length) to produce a contraction.
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